Vulcanizing apparatus



March 17, 1925. 1,530,255

W. FROST vuLcANIzING/APPARATUS' Filed Nay 6, 1922 vio Patented Mar. 17, 1925.

enrEN'rv ortica;

WILLIAM Pri-ose, or Lennon, ENGLAND, Assrenon To HARVEY FROST a COMPANY,

` LIMITED, oPLoNnON, ENGLAND. v l

VULGANIZING APPARATUS.

Application filed May 6,

Im arorei'nents in Vulcanizinv A. )aratus of which the following` is a specification.

rFhis invention is for improvements in or relating to vulcanizing apparatus and has for its object to provide an improved coiistruction of apparatus whereby theprocess is simplified, particularly as regards the heat treatment. As is well known, the process of vulcanizing requires that the material shall beheated to a definite temperature, and `maintained at that temperature for a definite period of time. Many fattem-pts have been made to'provide a heating unit which shallbeinore orless automatic in its action, in so far as the ycont-rol of the temperature iscOnCerned; it is also desirable, in order-to savetime, that heat should be supplied quickly to the material to'raise it to the required temperature, and that the supply of heat should then be reduced in .order that it may be maintained atfthat temperaturewithout any further rise.

W'ith these objects in view, there is provided, according to this invention, in vulcanizing apparatus, a heating unit comprising a thermal storage element which,-when heated to a temperature notless than that required for vulcanizing, .is'of such a heat capacity that it can heat up the material to lbe vulcanized and maintain it at not less than vulcanizing temperature for substantially not more t-han'the'requisite periodof time, upon the expiry of which time the temperature of the element will have fallen below that required for vulcanizing.

According' to yet another feature of this invention, the thermal storage unit aforesaid is made of such` a weight, in relation to the area of its base that when merely laid upon the article which is to be vulcanized itexerts the requisite pressure upon it.. This construction is particularly suitable when dealing with articles such as the inner, tubes of tires, which, when being repaired, require treatment over a comparatively small area, andl which can be simply laid on a table for lsuch treatment. Obviously, however, the heat storage element couldibe of any other shape to suit any 'special class of work. The gure is a diagrammatic sectional View 1922. senai No. 559,025;

through oneform of an apparatus according to the invention. i

In the specific embodiment of this iiiveiition,the hea-ting unit is constituted by aA preferably closed vessel 5f whereof rone of the outer walls 6 is shaped in any desired manner to serve as the hot surface against which the material 7 to be vulcanized is held.' The remaining surface of the vessel may- `be provided with vsuitable heat-insulating material 8' to reduce the amount of heat which is wasted or lost by radiation or conduction. This vessel contains a suitable quantity lof material 9 which is selected so astov have a suitable heat capacity as above set forth. This material may be one which is solid at ordinary atmospheric temperatures, .and is liquefied when heated to a tem- -perature not less than that necessary for.

vuleanizing,l and preferably at a temperature not greatly in excess of that required; `byfvvayzof example of such materials, it may be stated that an alloy of v21% cadmium and 79% bismuth meltsat about295o F.; or ain- `monium sulphate melts at 2840` F. orv animoiiium nitrate melts atfB'lQ'"l F.

The method of rising the unitis to heat it in a separate furnace, oven or the like,

-and when -it has attained the desired temperature it is removed and the material 7 to` I be vulcanized is applied to the heating surface 6 .of the unit. It thereupon absorbs heat from the unit, and in the caseof a substance 9 which is liquefied as above state-d,4 the heat rst absorbed is a comparatively small amount Whilst the liquidy is cooling to its melting point, and thenthe liquidgives up its latent heat Without further fall of temperature. As soon as the material 9 has become entirely solid, its temperature falls on thek further extractionr of heat, and the total heat capacity kof the heating unit is so selected that this fall of temperature brings the heating unit below vulcanizing temperature at about the time that the process of v'ulcanizing has been completed. lt will be appreciated that the further extractionvof heat above referred to consists mainly of the losses'bv conduction, radiationand 'convection which ensue inthe ordinary working of the apparatus. In order to neutralize as far as possible the variations lin the external conditions which would e'ect the `rate of this heat loss, itis de-v lll sirable that the thermal storage unit should be ettectively thern'ially insulated, except on the surface to which the material is applied, Obviously, the provision ot this insulation 8 leads also to economy in heat consumption. The whole heat treatment can, theretore, be entirely automatic, since the temperature can be controlled by selecting a material 9 having the desired melting point, and the period ot time before the tem perature tails below that necessary for vulcanizing can be determined by suitably selecting the heat capacity and the thermal insulationA oit the whole unit.

lVhilst an arrangement such as that above mentioned will generally be the most convenient for use, it also lies within the scope of this invention to utilize the latent heat otl evaporation of a suitable liquid in the container, instead oit the latent heat of fusion in a solid. It will be appreciated that the range ot' liquids which may be selected is not limited to the same extent as is that ot the alloys or solids, since the boiling` point of the liquid which is the point at which it absorbs and gives up its latent heat can be controlled according to the pressure to which it is subjected. In manufacturin g a thermal storage unit, using liquid, it is desirable to provide only such a quantity of liquid in a closed container 5 as will be entirely evaporated at a temperature notL substantially in excess 'of that appropriate `to vulcanization, as there is thereby provided a condition of a'lipairs which tends to prevent the storage unit from attaining an excessive temperature.

According to another feature ot the invention, the material which is liquefied or vapourized may be such that when it is in the solid or liquid state respectively, it is a poor conductor ot heat, such tor example as a material. ot the nature ot wax. So long` as the material is liquid, the convection currents set up in it during its cooling enable it to impart its heat easily to the material which is being vulcanized, but when the material commences to solidify it is a poor conductor ot heat and it therefore gives up its heat more slowly. This is advantageous in that the heatV is given up rapidly during the period of raising the temperature ot the rubber which is to be \\'ul.canized, and the subsequent rate of transmission of heat is automatically reduced in accordance with the reduced requirements, since it is only necessary to supply enough heat to compensate for the losses by radiation and conduction 'from the rubber to maintain it at the vulcanizing temperature.

It will be appreciate-d that in using a thermal storage unit. in which the heat is stored as latent heat, the duration 4oi the time o'lf solidiication, which is the time during which the ten'iperature remains substantially constant, can be determined by selecting the amount ot material which is liquefied, or oit' liquid which is vaporized, since the amount ot heat which is given out at a steady temperature during soliditication directly proportioned to the weight ot material which has been liquefied.

It may also be desirous in some instances to use two ditiierent substances or alloys which melt at different temperatures, so that two ditlierent periods ot' uniform temperature can be obtained during the cooling o't` the element, such periods giving respectively the temperatures otthe different substances which have been melted, and in some instances it may be convenient to use a mixture which gives eutectic alloys at appropriate ten'iperatures.

that l claim as my invention and desire to secure by Letters Patent is:

l.. ln vulcanizing apparatus, a l'ieating unit comprising a thermal storage element which, when heated to a temperature not less than that required 'for vulcanizing, is ot such a heat capacity in relation to the material to be vulcanized that it can heat up the said material and maintain it at not less than vulcanizing temperature for substantially not more than the requisite period ot time, upon the expiry of which time the temperature ot' the element will have fallen below that required for vulcanizing, which element contains a material that is normally a poor conductor of heat and that changes its state when heated to a temperature not less than that required for vulcanizing, whereby heat is stored in it as latent heat.

2. lin vulcanizing apparatus, a heat-ing unit comprising a thermal storage element which, when heated to a temperature not less than that required tor vulcanizing, is ot such a heat capacity in relation to( the material to be vulcanized that it can heat up the said material and maintain it at not less than vulcanizing temperature Yfor substantially not more than the requisite period of time, upon the expiry of which time the temperature ot' the element will have fallen below that required for vuleanizing, which element contains a plurality ot materials which will change their state at different temperatures, each oi. which temperature is appropriate to the process ot vulcanization, whereby heat is stored inA the element as latent heat. l

In testimony whereof I attbi my signature.

WILLIAM rnosr. 

